The present invention relates to a process for producing a semiconductor integrated circuit device, and, more particularly, the invention relates to a technique that is effective for application to production of a semiconductor integrated circuit device having an MOSFET (metal oxide semiconductor field effect transistor) of a polymetal structure, in which a gate electrode is constituted with a laminated film of polycrystalline silicon containing boron (B) and a refractory metal.
Japanese Patent Laid-Open No. 132136/1984 (hereinafter referred to as "Kobayashi 1") discloses a technique in which, after forming a gate electrode of a polymetal structure containing a W film or an Mo film on an Si (silicon) substrate, light oxidation is carried out in a mixed atmosphere of steam and hydrogen to selectively oxidize only Si without oxidizing the W (Mo) film. This utilizes characteristics in which the steam/hydrogen partial pressure ratio, at which the redox reaction is at equilibrium, is different between W (Mo) and Si, and the selective oxidation of Si is realized in such a manner that the partial pressure ratio is set in a range in which, when W (Mo) is oxidized, it is immediately reduced with co-existing hydrogen, but Si remains as being oxidized. The mixed atmosphere of steam and hydrogen is formed by a bubbling method, in which a hydrogen gas is supplied into pure water contained in a container, and the steam/hydrogen partial pressure ratio is controlled by changing the temperature of the pure water.
Furthermore, other principal publications relating to selective oxidation by a group of the inventors of the above described subject matter include Japanese Patent Laid-Open No. 89943/1985 (hereinafter referred to as "Kobayashi 2") and Japanese Patent Laid-Open No. 150236/1986 (hereinafter referred to as "Iwata").
Japanese Patent Laid-Open No. 94716/1995 (hereinafter referred to as "Muraoka") discloses a technique in which, after forming a gate electrode of a polymetal structure containing a metal nitride layer, such as TiN, and a metal layer, such as W, on an Si substrate via a gate oxide film, light oxidation-is carried out in an atmosphere of a reducing gas (hydrogen) and an oxidative gas (steam) diluted with nitrogen. According to the this technique, it is found that only Si can be selectively oxidized without oxidizing the metal layer, and oxidation of the metal nitride layer can also be prevented because the denitrification reaction from the metal nitride layer is prevented by diluting the steam/hydrogen mixed gas with nitrogen.
In Series of Theses of 45th Symposium of Semiconductor Integrated Circuit Techniques, held on Dec. 1 and 2 of 1992, pp. 128 to 133, (hereinafter referred to as Nakamura) there is disclosed a technique for forming an oxide film in a strong reducing atmosphere containing steam synthesized by a stainless catalyst.